This invention relates to sub-sea wells and more particularly to adjustable conductor guides and methods and tools for adjustment thereof.
Early offshore production can be achieved by means of the template tieback system, wherein development drilling and platform construction can run concurrently. Development wells are pre-drilled through a sub-sea template from a floating rig and the wells tied back to the production platform following its installation over the template. The major advantage of the tieback concept is that return on investment can be quicker than for wells drilled conventionally from a fixed platform.
There is a risk of misalignment when the platform is positioned over the template. The risk increases at greater water depths and is such that the ultimate success of a drilling venture may be vitiated by positional inaccuracies with substantial loss of investment.
The Applicants' studies in this field have indicated that the main cause of failure is likely to be excessive bending stresses in the tieback conductor. This bending stress depends partly on lateral offset between platform and well head, angular offset, and "environmental loadings". By way of example, it may be necessary to maintain the platform vertical to within .+-.0.5.degree. and lateral misalignment within .+-.0.65 m (.+-.26"): these figures are given by way of example only.
The invention accordingly provides a conductor guide assembly comprising an outer ring supporting an inner guide, the axes of ring and guide being spaced apart. The ring is mounted on the platform about an aperture and the platform is positioned over the template so that as far as possible the aperture is vertically aligned with the well head. Rotation of the assembly in the aperture moves the axis of the inner guide in relation to the well head axis and enables any spacing between those axes to be minimized.
Conveniently means are provided on the outer ring for location with respect to the aperture in one of a number of possible angular positions. Preferably means are provided on the outer ring for rolling contact with an annular area about the aperture to resist upward force on the assembly.
Turning broadly to the method aspect, the invention provides a method of aligning with a sub-sea well head, a conductor guide mounted in a platform above the well head, the conductor guide being the inner guide of an assembly comprising an outer ring supported in an aperture in the platform and said inner guide supported eccentrically thereon, the method comprising the steps of:
(a) lowering through the guide an adjusting tool having a projection to extend substantially to the well head; PA1 (b) by means of the adjusting tool, rotating the conductor guide assembly in its aperture to bring the axis of the inner guide as near as possible into alignment with the well head; and PA1 (c) locking the conductor guide assembly in angular position within the aperture and removing the adjusting tool. PA1 (a) a body adapted to enter and locate in the inner guide of the assembly, the body having a generally vertical first axis coincident with that of the inner guide on location therein; PA1 (b) means for establishing coincidence of the first axis with that of a well head; PA1 (c) means for connecting a drill pipe to the body and aligning the pipe, when the body is located in the inner guide, selectively with the axis of the inner guide and the axis of the outer ring; PA1 (d) means to land the body on the assembly and to lock the body thereto for movement together,
Preferably the tool is lowered, manipulated and subsequently removed by drill string. The adjusting tool can be rotated first on the axis of the inner guide to engage means to lock the tool to the guide, and then on the axis of the outer ring to rotate the tool and assembly as one.
In a preferred system, the tool has a body to locate in the inner guide and to lock releasably thereto for rotation of the assembly, and the drill string is connected to a block mounted on the body and rotatable with respect thereto between limits and lockable thereto. In this preferred system, the method of the invention further comprises the steps of rotating the drill string to move the block with respect to the body to a limit position where the string axis coincides with that of the inner guide, further rotating the drill string thereby to lock the body to the inner guide, rotating the drill string back to another limit position where the string axis coincides with the axis of the outer ring, lifting the string to lock the block to the body and release the assembly for rotation, and thereafter rotating the tool and assembly as one.
As above indicated the invention also provides a tool for use in the system described. In a preferred form the invention provides a tool for adjusting a conductor guide assembly comprising an outer ring supporting an inner guide, the axes of ring and guide being spaced apart, comprising:
whereby on landing the body in the inner guide rotation thereof by rotation of the drill string on the inner guide axis locks the body to the assembly whereupon the drill string may be rotated on the axis of the outer ring to bring the axis of the inner guide as near coincident with the well head as possible.
The main object of the invention is to provide a conductor guide system which allows of some wider tolerance in positioning the platform over the template.
Another object is to provide an improved conductor guide assembly for a sub-sea well head which is easily and quickly aligned with the sub-seal well head.
A further object is to provide an improved method of aligning a conductor guide with a sub-sea well head which can be readily operated from the surface and ensures proper alignment.
Still another object is to provide an improved tool for adjusting the sub-sea conductor guide assembly into aligned position from the surface and to lock the assembly in aligned position.